Saturday, July 31, 2010

New Meets Old

The Pine Grove covered bridge is immediately downstream from the Chester County water plant and sets the tone for this place where old and new seem to meet and blend. But even part of the old is a facade. The covered bridge was rebuilt atop steel beams. I slid into the water at the downstream end of a large pool just around the first bend downstream from the bridge. Corixids, which are flying insects with the ability to swim, feed off the bacterial algal ooze that accumulates on the bottom of the slow moving backwater. I have never seen these animals in the wild, only in swimming pools, and their mottled tan wing covers are much more attractive here. The rocks in the main flow are all covered in sponges infused with sand and sediment so they aren’t so obvious until they are touched. I was transfixed by the concept of freshwater sponges since I studied streams in high school. My teachers told me about a patch of them in a local stream, but I was never able to locate them. When I think of sponges I think of marine systems, and this was part of my amazement. Now, 30 years later, I finally find some freshwater sponges, but they are nothing like the animal I had pictured: upright typical sponge form. Instead, they are encrusting and dirty with silt and sand. Ancient organisms covered by the new problems of sedimentation and increased scouring flows. A young eel hunted between rocks on the bottom unaware of my presence and a small northern water snake swam over my left shoulder and under my right arm as I tried to snap a picture of the eel. A Chinese mystery snail lay upside down and was encrusted into the bottom by sponges. These invasive snails have the ability to filter feed, and I wonder if that is what this one was doing. It found a safe place in the stream bed, was protected by encrusting sponge and filter fed for food. New biology, in the form of a recent addition to our aquatic systems, the Chinese mystery snail, and old biology in the form of freshwater sponge meet and become intimately associated here, like the covered bridge and water treatment plant.